Angle Kappa Measurements: Normal Values in Healthy Iranian Population Obtained With the Orbscan II

A comparative study of pupil offset measurement using Pentacam and Keratron Scout in myopic young adults

CLINICAL RELEVANCE

Assessing the consistency of pupil offset measurements between the Pentacam and Keratron Scout is essential for the refractive surgery design of young myopic patients.

BACKGROUND

Accurate preoperative measurement of pupil offset is critical to achieving a better quality of vision after refractive surgery. The Pentacam and Keratron Scout are commonly used in hospitals, and evaluating their consistency is essential for accurate measurement of pupil offset.

METHODS

Six hundred eyes (600 subjects) were included in this study. Pupil offset and its X, Y-component were measured by Pentacam and Keratron Scout, respectively. Agreement and repeatability between the two devices were identified by intraclass correlation coefficient and Bland-Altman plots with 95% limits of agreement. Paired t-tests and Pearson analysis were used to compare the differences and correlations between the two devices.

RESULTS

The mean age of all subjects was 23 ± 5 years. The mean pupil offset magnitude obtained from Pentacam and Keratron Scout was 0.16 ± 0.08 mm and 0.15 ± 0.07 mm. The 95% limits of agreement (-0.11-0.13, -0.09-0.11, and -0.11-0.12) and intraclass correlation coefficient (0.82, 0.84, and 0.81) demonstrated good agreement and repeatability of the two devices in measuring pupil offset and its X, Y-component. A significant correlation between the two devices was found (r = 0.71, 0.73, and 0.70). The direction of pupil offset measured by the devices was both predominately towards the superonasal quadrant.

CONCLUSION

Pentacam and Keratron Scout showed good agreement in measuring pupil offset and its X, Y-component, which can be used interchangeably in clinical practice.

Angle Kappa Influence on Multifocal IOL Outcomes

PURPOSE

To characterize angle kappa and study the relationship between preoperative angle kappa and postoperative refractive accuracy, visual outcomes, and patient satisfaction in a large population of eyes with multifocal intraocular lens (MIOL) implantation.

METHODS

A comprehensive electronic medical record chart review of 26,470 consecutive eyes that underwent immediate sequential bilateral cataract or refractive lens exchange with MIOLs was conducted. The primary outcome measures were postoperative monocular uncorrected distance visual acuity (UDVA), manifest refraction sphere and cylinder, spherical equivalent (SEQ), defocus equivalent (DEQ), subjective quality of vision at near, intermediate, and distance, and the likelihood of recommending the procedure. Relationships between preoperative angle kappa and postoperative outcomes were assessed with Pearson correlations.

RESULTS

Angle kappa followed a right-skewed normal distribution (R2 = 0.99) with a mean ± standard deviation of 0.64 ± 0.27 mm. No clinically meaningful relationship was found between preoperative angle kappa and postoperative sphere, cylinder, SEQ, and DEQ, all with R2 ⩽ 0.0005. Similarly, there was no clinically meaningful relationship between preoperative angle kappa and postoperative UDVA (R2 = 0.001), postoperative satisfaction for near, intermediate, and distance vision (all R2 ⩽ 0.0023), or for recommending the MIOL surgery to friends and relatives (R2 = 0.0000).

CONCLUSIONS

Preoperative angle kappa does not have a predictive clinical impact on postoperative MIOL visual outcomes, refractive accuracy, or subjective patient satisfaction. Angle kappa as a single variable cannot be used to determine MIOL candidacy. [J Refract Surg. 2023;39(12):840-849.].

Assessment of Pupil Size and Angle Kappa in Refractive Surgery: A Population-Based Epidemiological Study in Predominantly American Caucasians

Purpose This retrospective study aims to establish normative values for pupil size, angle kappa, higher-order aberration, and astigmatism type in a largely Caucasian population in Utah, United States, utilizing the NIDEK OPD-Scan III system (Gamagori, Japan). Methods This study included 716 patients (1432 eyes) grouped based on spherical equivalence and age. Measurements were conducted under mesopic and photopic conditions. Statistical analysis involved Pearson's correlation and linear regression using the generalized estimating equation. NIDEK OPD-Scan III measured mesopic and photopic pupil size and angle kappa. The subjects were then grouped based on their spherical equivalence in diopters (D) and age in decades. The spherical equivalence groups were defined: >-6 D, -5.99 to -3 D, -2.99 to -0.25 D, -0.24 to 0.24 D, and >0.25 D (range 0.25-5.75 D). The higher-order aberration groups were based on the reason for the visit: laser-assisted in situ keratomileusis, photorefractive keratectomy, and small incision lenticule extraction as one group; cataract evaluation; and keratoconus. Astigmatism measurements were grouped into with-the-rule (WRT), against-the-rule (ATR), and oblique astigmatism, with further subgrouping into a young cohort (20-40 years) and an old cohort (>65 years).  Results Among 716 participants, 49.2% were men; the mean age was 42.1±15.5 (range 7-88 years). The average spherical equivalence for myopia eyes was -3.28±2.34 D, and 1.51±1.46 D for hyperopia eyes. The mean mesopic pupil size was 5.68 ± 1.09 mm; the photopic pupil size was 4.65±1.09 mm. Pearson's correlation coefficient for mesopic pupil size versus age was -0.551, and -0.42 for photopic pupil (p < 0.001); sphere vs mesopic pupil size was -0.200, and -0.173 for photopic pupil (p < 0.001). The regression analysis for mesopic pupil size versus age revealed a 0.39 mm decrease in average pupil size per decade increase in age, and 0.25 mm decrease per decade for photopic pupil. The regression analysis for mesopic pupil size versus sphere revealed a 0.22 mm decrease in average pupil size per 3D increase in sphere, and a 0.16 mm decrease 3 D increase in sphere for the photopic pupil. The mean mesopic angle kappa was 0.33 ± 0.15 mm; photopic angle kappa was 0.31±0.15 mm. Pearson's correlation coefficient for mesopic angle kappa vs spherical equivalence was 0.32, and 0.296 for photopic angle kappa (p <0.001 for both). Regression analysis for mesopic angle kappa vs spherical equivalence demonstrated a 0.051 mm increase in angle kappa per 3 D increase in spherical equivalence, and a 0.048 mm increase for photopic angle kappa (p < 0.001 for both). Among the higher-order aberration groups, the keratoconus group exhibited the highest levels. In terms of astigmatism type, WRT astigmatism was the most common in the young cohort, while ATR astigmatism was most prevalent in the older cohort. Conclusions The results of this study reveal significant associations between pupil size and increasing age, as well as between pupil size and increasingly positive refractive errors. These findings hold particular clinical relevance to older patients and individuals with hyperopia, as they undergo photoablative corneal refractive surgery or multifocal intraocular lens implantation. Understanding the established normative values for pupil size, angle kappa, higher-order aberration, and astigmatism type can aid clinicians in making more informed decisions and improving patient outcomes.

Distribution of angle lambda and pupil offset as measured by combined Placido Scheimpflug Topography

BACKGROUND

Angle lambda is the angle between the pupillary axis and the line of sight. It is important for accurate centration during anterior segment surgery. The purpose of this study is to identify the distribution of angle lambda and pupil center offset as measured by a combined placido disc Scheimpflug topography system.

METHODS

A prospective non-randomized study was performed on 2178 eyes in Eye World Hospital, Giza, Egypt. Sirius device (CSO, Costruzione Strumenti Oftalmici, Florence, Italy, version 3.2.1.60) was used to measure average keratometry (K), anterior chamber depth (ACD), central corneal thickness (CCT), horizontal visible iris diameter (HVID), pupil radius (PR), pupil center intercept x-component (PCI-x), and pupil center intercept y-component (PCI-y). Axial length (AL) was measured by immersion A-scan Eyecube Ultrasonography device (Ellex, Adelaide, South Australia, Australia). Angle lambda was calculated by a trigonometrical equation. Pearson correlation was used to analyze the correlation between angle lambda and age and refraction.

RESULTS

Average angle lambda in all eyes was 3.32° ± 1.99. Mean angle lambda was significantly smallest in myopia and largest in hyperopia. Age correlation to angle lambda was insignificant. Average PCI-x and PCI-y in all eyes was - 0.047 mm and + 0.091 mm, respectively.

CONCLUSIONS

Angle λ is significantly larger in hyperopia than myopia, and the effect of age is insignificant. Pupil center offset was horizontally greater in hyperopia than in myopia. We therefore encourage the preoperative assessment of angle λ to avoid decentered ablation, especially when treating hyperopia.

Angle Kappa agreement between Scheimpflug tomography, combined placido Scheimpflug and combined slit scanning placido systems

PURPOSE

To compare the measured or calculated angle Kappa using Oculus pentacam HR, Sirius and Orbscan III devices.

PATIENTS AND METHODS

A prospective randomized cohort study, conducted on 47 eyes of 47 healthy orthotropic individuals, with an age range of 18-50 years and a corrected Snellen's distance visual acuity (CDVA) of 0.8 decimal or better. Angle Kappa is assessed directly using Orbscan® III software version 1.8.165.1. (Bausch and Lomb Rochester, New York, United States), while Pentacam® HR 1.21r.65 (Oculus Optikgeräte GmbH, Wetzlar, Germany) and Sirius device (CSO, version 3.2.1.60, Costruzione Strumenti Oftalmici, Florence, Italy) were used to calculate angle kappa indirectly.

RESULTS

Least mean difference of estimated angle Kappa was between Orbscan and Pentacam devices (- 0.18° ± 1.8), and it was statistically insignificant (p value = 0.1294). Differences between both Orbscan and Sirius, and Pentacam and Sirius were statistically significant (p value = 0.0004 and < 0.0001 consecutively). Bland Altman analysis showed a 95% confidence interval between Orbscan III and Pentacam of - 3.76 to 3.4 and between Orbscan III and Sirius of - 3.79 to 2.26.

CONCLUSION

Pentacam parameters can be used as a reliable method to calculate angle kappa indirectly, without usage of any additional measurements from other machine. Sirius device parameters could also be used, but with less accurate results. A simple modification to those devices' software to calculate it, and incorporate it in the printout is possible, and highly recommended.

Comparison of preoperative angle kappa measurements in the eyes of cataract patients obtained from Pentacam Scheimpflug system, optical low-coherence reflectometry, and ray-tracing aberrometry

Background

Angle kappa plays a vital role in the implantation of multifocal intraocular lens (MIOL). Large angle kappa is related to a higher risk of postoperative photic phenomena. This study aims to compare preoperative angle kappa in the eyes of cataract patients obtained from the Pentacam Scheimpflug system (Pentacam), optical low-coherence reflectometry (Lenstar), and ray-tracing aberrometry (iTrace).

Methods

One hundred thirteen eyes of 113 patients with cataracts were included. Each eye was examined 3 times using all devices to obtain angle kappa and pupil diameter. When considering dependent eyes for one individual, angle kappa in both right eyes and left eyes should be analysed separately. The repeatability and reproducibility were evaluated using the within-subject standard deviation (Sw), repeatability (2.77 Sw), and intraclass correlation coefficient (ICC). The difference, correlation, and agreement between devices were evaluated by paired t-tests, Pearson tests, and Bland-Altman analysis, respectively.

Results

Intraoperator repeatability and interoperator and intersession reproducibility of angle kappa showed an Sw of less than 0.05 mm, a 2.77 Sw of 0.14 mm or less, and an ICC of more than 0.96. Angle kappa was not significantly different between Pentacam and Lenstar (P > 0.05), while angle kappa was significantly different between Pentacam and iTrace and between Lenstar and iTrace (P < 0.05). There was a strong correlation between Pentacam and Lenstar for angle kappa (r =0.907 to 0.918) and a weak or moderate correlation between Pentacam and iTrace and between Lenstar and iTrace (r =0.292 to 0.618). There were narrow 95% limits of agreement (LoA) between Pentacam and Lenstar for angle kappa and wide 95% LoA between Pentacam and iTrace and between Lenstar and iTrace. No significant differences in pupil diameter were found between Pentacam and Lenstar in either eye (P > 0.05). Positive angle kappa (nasal light reflex) was found in most cataract patients (79.25% to 84.91%) through 3 different devices in both eyes.

Conclusions

The 3 devices provided high intraoperator repeatability and interoperator and intersession reproducibility for angle kappa measurements. The measurement of preoperative angle kappa in the eyes of patients with cataracts by Pentacam and Lenstar has good agreement.

Distribution of Pupil Offset and Angle Kappa in a Refractive Surgery Preoperative Population of 750 Myopic, Emmetropic, and Hyperopic Eyes

PURPOSE

To report the distribution of pupil offset and angle kappa in 750 myopic, emmetropic, and hyperopic eyes presenting for refractive surgery.

METHODS

A retrospective study included 750 consecutive eyes screened for corneal refractive surgery between January 2006 and February 2013. The eyes were divided into three equal groups based on manifest refraction spherical equivalent (SEQ): emmetropic group between -0.25 and +0.50 diopters (D) and cylinder up to 1.00 D, myopic group greater than -0.50 D, and hyperopic group greater than +0.50 D. Angle kappa was measured with the Orbscan II software (Bausch & Lomb, Inc) and pupil offset defined as the distance at the corneal plane between the corneal vertex and the pupil center. Correlations with SEQ, cylinder, scotopic pupil diameter, average keratometry, and age were performed.

RESULTS

All results are reported for myopic, emmetropic, and hyperopic groups, respectively. Mean SEQ was -4.84 ± 2.89 D (range: -0.88 to -14.00 D), +0.21 ± 0.23 D (range: -0.25 to +0.50 D), and +2.44 ± 1.58 D (range: +0.63 to +7.75 D). Mean pupil offset magnitude was 0.27 ± 0.14 mm (range: 0.00 to 0.68 mm), 0.34 ± 0.14 mm (range: 0.02 to 0.78 mm), and 0.39 ± 0.13 mm (range: 0.07 to 0.75 mm). Mean pupil offset X-component was -0.18 ± 0.18, -0.28 ± 0.16, and -0.34 ± 0.15 mm (temporally displaced from the corneal vertex). Mean pupil offset Y-component was 0.06 ± 0.15, 0.03 ± 0.16, and 0.01 ± 0.16 mm (superiorly displaced from the corneal vertex). Multivariate linear regression for pupil offset magnitude found statistically significant variables were SEQ, cylinder, scotopic pupil diameter, and average keratometry. For pupil offset X-component, significant variables were SEQ, cylinder, and scotopic pupil diameter. For pupil offset Y-component, significant variables were SEQ and scotopic pupil diameter. Mean angle kappa was 5.28 ± 1.49°, 6.14 ± 1.44°, and 5.77 ± 1.29°.

CONCLUSIONS

Contrary to common belief, a pupil offset is present in the vast majority of eyes regardless of refractive error, with the mean temporal offset of at least 0.18 mm. Confirming previous studies, the largest pupil offset was found in the hyperopic group. However, there was also a wide range of pupil offset in myopic and emmetropic eyes. Correlations with SEQ and keratometry support the theory that pupil offset is also correlated with axial length. [J Refract Surg. 2021;37(1):49-58.].

Changes of angle Kappa and corneal morphology changes in myopic patients after SubBowmanKeratomileusis

OBJECTIVES

To investigate angle Kappa and diopter distribution in myopic patients and the changes of angle Kappa and corneal morphology after Sub-Bowman-Keratomileusis (SBK), and to analyze the effects of the surgery on corneal morphologic changes and the patients' near fixation characteristics.

METHODS

The clinical data of 134 myopic patients (268 eyes) undergoing SBK from August 2015 to August 2016 were retrospectively analyzed. Angle Kappa, corneal curvature in the central corneal region of 3 mm, and post-corneal Diff value were measured by Orbscan IIz Corneal Topography System before operation, 1 month and 6 months after operation. According to the values of angle Kappa before SBK, the patients were divided into 2 groups: the large K group (angle Kappa≥5°, 71 eyes) and the small K group (angle Kappa<5°, 197 eyes). Correlation analysis of the factors influencing angle Kappa at 6 months after operation was performed.

RESULTS

In the large K group, angle Kappa was (5.67±0.65)°, spherical equivalent was (-4.84±2.32) D, and angle Kappa was decreased after operation (both P<0.05) with the increased decreasing range over time. In the small K group, angle Kappa was (3.51±1.08)°, spherical equivalent was (-5.78±2.63) D, angle Kappa was increased after operation with decreased increasing range over time, and the difference was statistically significant between 6 months after operation and before operation (P<0.05).The post-corneal Diff value of the 2 groups was increased after operation (all P<0.001), and was decreased from 1 month to 6 months after surgery. The corneal curvature in the central corneal region of 3 mm of the 2 groups 1 month after operation was decreased significantly (both P<0.001). From 1 month to 6 months after operation, the corneal curvature of the large K group tended to be stable, while the corneal curvature of the small K group tended to increase. There was no significant correlation between the changes of angle Kappa 6 months after operation and the changes of the corneal central curvature or the post-corneal Diff value (both P>0.05), but the changes of angle Kappa 6 months after operation was positively correlated with corneal cutting thickness (rlarge K group=0.398, rsmall K group=0.218, both P<0.05) and it was negatively correlated with preoperative diopter (rlarge K group=-0.283, rsmall K group=-0.233, both P<0.05).

CONCLUSIONS

The angle Kappa is decreased in low-moderate myopia patients with large angle Kappa, while is increased in high myopia patients with small angle Kappa after SBK. Myopia patients after SBK will look for the new balance of the binocular accommodation and vergence function for improving the comfort in the near-work situations.

Determination of Optic Axes by Corneal Topography among Italian, Brazilian, and Chinese Populations

This study aims to describe a new universal method to identify the relative three-dimensional directions of visual, pupillary, and optical axes of the eye and the angles between them using topography elevation data. The method was validated in a large clinical cohort, and ethnical differences were recorded. Topography elevation data were collected from 1992 normal eyes of 966 healthy participants in Italy, Brazil, and China. The three main axes were defined as follows: optical axis (OA) was defined as the optimal path of light that passes through the ocular system without refraction. The pupillary axis (PA) line was defined using X and Y coordinates of the pupil centre with the chamber depth, in addition to the centre of a sphere fitted to the central 3 mm diameter of the cornea. The visual axis (VA) was taken by its best approximation, the coaxially sighted corneal light reflex. The alpha angle was measured between the VA and OA, and the kappa angle between the VA and PA. The average values of kappa and alpha angles were 3.41 ± 2.84 and 6.04 ± 2.43 in the Italian population, 2.6 ± 1.53 and 5.87 ± 2.3 in the Brazilian population, and 2.09 ± 1.22 and 3.85 ± 1.48 in the Chinese population.

Adduction-Induced Strain on the Optic Nerve in Primary Open Angle Glaucoma at Normal Intraocular Pressure

PURPOSE/AIM

The optic nerve (ON) becomes taut during adduction beyond ~26° in healthy people and patients with primary open angle glaucoma (POAG), but only retracts the globe in POAG. We used magnetic resonance imaging (MRI) to investigate this difference.

MATERIALS AND METHODS

MRI was obtained in 2-mm quasi-coronal planes in central gaze, and smaller (~23-25°) and larger (~30-31°) adduction and abduction in 21 controls and 12 POAG subjects whose intraocular pressure never exceeded 21 mmHg. ON cross-sections were analyzed from the globe to 10 mm posteriorly. Area centroids were used to calculate ON path lengths and changes in cross-sections to calculate elongation assuming volume conservation.

RESULTS

For both groups, ON path was nearly straight (<102.5% of minimum path) in smaller adduction, with minimal further straightening in larger adduction. ON length was redundant in abduction, exceeding 103% of minimum path for both groups. For normals, the ON elongated 0.4 ± 0.5 mm from central gaze to smaller adduction, and 0.4 ± 0.5 mm further from smaller to larger adduction. For POAG subjects, the ON did not elongate on average from central gaze to smaller adduction and only 0.2 ± 0.4 mm from smaller to larger adduction (P = .045 vs normals). Both groups demonstrated minimal ON elongation not exceeding 0.25 mm from central gaze to smaller and larger abduction. The globe retracted significantly more during large adduction in POAG subjects than normals (0.6 ± 0.7 mm vs 0.2 ± 0.5 mm, P = .027), without appreciable retraction in abduction. For each mm increase in globe axial length, ON elongation in large adduction similarly increased by 0.2 mm in each group.

CONCLUSIONS

The normal ON stretches to absorb force and avert globe retraction in adduction. In POAG with mild to severe visual field loss, the relatively inelastic ON tethers and retracts the globe during adduction beyond ~26°, transfering stress to the optic disc that could contribute to progressive neuropathy during repeated eye movements.

Optic Nerve Traction During Adduction in Open Angle Glaucoma with Normal versus Elevated Intraocular Pressure

Purpose/Aim: We used magnetic resonance imaging (MRI) to investigate effects of intraocular pressure (IOP), race, and other factors on optic nerve (ON) traction in adduction, a phenomenon proposed as neuropathic in open angle glaucoma (OAG).Materials and Methods: Thirty-five patients with OAG (26 with maximal untreated IOP ≤21 mmHg, 9 with IOP >21mmHg) and 48 controls underwent axial and quasi-coronal MRI in central gaze and large (27-33°) abduction and adduction. Some underwent MRI at smaller ductions (21-28°). Effects of presence vs. absence of OAG; within OAG whether maximum IOP level was ≤21 mmHg vs. >21 mmHg; adduction angle; race; age; and gender on ON path length and globe translation were analyzed using generalized estimating equations to account for possible intereye correlations of individual subjects.Results: Average visual field mean deviation (±standard error of mean, SEM) was -8.2 ± 1.2 dB in OAG with normal IOP, and -6.1 ± 1.4 in high IOP. In central gaze, ON path in OAG was significantly more redundant than in controls but in both groups the ON became significantly and almost equally straighter in small (~21°) or large (~27°) adduction than in central gaze. With progressive adduction only, globes retracted in OAG (P < 0.005) but not in controls; this was only weakly related to globe size and not to IOP elevation. Globe retraction in adduction was significant only in OAG, and in that group was significantly greater in Asian than white patients (P < 0.02).Conclusions: Although ON tethering in adduction is normal, progressive adduction is associated with abnormal globe retraction in OAG regardless of IOP level. This phenomenon is more prominent in Asians who have OAG. Traction in adduction may cause repetitive strain injury to the ON and peripapillary sclera, thus contributing to the optic neuropathy of glaucoma independent of IOP.

Functional anatomy of extraocular muscles during human vergence compensation of horizontal heterophoria

We employed magnetic resonance imaging to quantify human extraocular muscle (EOM) contractility during intermittent convergent and divergent strabismus with each eye viewing monocularly at 20 cm compared with centered target fusion. Contractility, indicated by posterior partial volume change, was analyzed in transverse rectus and in medial and lateral superior oblique (SO) muscle compartments. In five subjects with intermittent esotropia, abduction of the deviated eye to monocular target fixation was associated with significant whole lateral rectus (LR) contraction, but with medial rectus (MR) relaxation that was significantly greater in the superior than inferior compartment. Esotropic eye abduction to binocular fusion was associated with similar relaxation in the two MR compartments, but with greater contraction in the LR's superior than inferior compartment. The whole diverging eye SO muscle relaxed. In three subjects with intermittent exotropia, converging eye fusional adduction was associated with significant whole LR relaxation and with MR contraction attributable to significantly greater contraction in the superior than inferior compartment. In adduction of the exotropic eye to monocular target fixation but not fusional adduction, the whole SO exhibited significant relaxation. Rectus pulley positions were not significantly altered by fusion of either form of intermittent strabismus. Globe rotational axis was eccentric in intermittent strabismus, rolling the eye so that rectus EOM lever arms facilitated vergence. These results confirm, and extend to fusion of intermittent horizontal strabismus, differential compartmental function in horizontal rectus EOMs and suggest a novel role for the SO in compensation of both intermittent esotropia and exotropia. NEW & NOTEWORTHY Disjunctive eye movements normally permit binocular fixation in near visual space but also compensate for mechanical imbalances in binocular alignment developing over the life span. Magnetic resonance imaging of the extraocular muscles demonstrates important differential function in muscle compartments during compensation of large-angle intermittent convergent and divergent strabismus in humans. Eye translation during rotation also enhances vergence compensation of intermittent strabismus.

Modified Krimsky test for irregular scarred corneas

The measurement of the amount and nature of deviation is the essence of diagnostic workup of a patient with strabismus and also has important therapeutic implications while planning the amount of surgery or prescribing therapeutic prisms. Although Krimsky test is a useful method, it cannot be used to measure deviation in patients with scarred and irregular cornea with an anechoic posterior segment making it difficult to see the corneal reflex. We hereby take the opportunity to present a modification of the original Krimsky test which is extremely helpful in determining the deviation in patients with irregular opaque corneas.